The PV yield is the amount of electricity your solar system produces in a year.

autarc calculates it for every hour of the year – depending on the location, the weather, the orientation, tilt and installed power of the modules, and shading from the terrain and objects.

These hourly values feed directly into the system simulation, where they determine self-consumption, battery charging and feed-in.

The calculation with PVGIS

The basis is PVGIS, the photovoltaic information system of the European Commission's Joint Research Centre. For your project's coordinates, PVGIS provides the irradiance and temperature for every hour of the year.

This is how autarc calculates the yield from it:

Group the modules: All modules with the same tilt and orientation are combined into one array – e.g. the east and west side of a gable roof become two arrays. The power of an array is the sum of the Pmax (STC) of its modules.
Irradiance per hour: For each array, PVGIS determines how much sunlight hits the tilted module surface in every hour – split into direct and diffuse light.
Yield per hour: From irradiance and temperature, PVGIS calculates the yield of crystalline silicon modules. Warm modules produce less than cold ones.
System losses: Losses for inverters, cables, module mismatch and soiling are deducted – 14 % by default. You can adjust the value under Settings > Products > PV-Planning.
Shading: PVGIS takes shading from the terrain (horizon) into account automatically. autarc additionally calculates shading from objects in your planning (see below).
Annual yield: The sum of all hourly values gives the monthly and annual yield you see in the PV planning under Production.

As weather data, PVGIS uses satellite data (SARAH-3) in Europe and Africa and global weather data (ERA5) outside this area. All values refer to the reference year 2023.

Shading from objects

Trees, chimneys, neighbouring buildings and other objects cast shadows on the modules during the day. For autarc to calculate this shading:

Model the surroundings – in one or more of these ways:
- Draw objects in the PV planning, e.g. Tree, Chimney, Fence, Wall or Carport.
- Turn on 3D Terrain on the 2D map. Hills, neighbouring buildings and trees from the terrain data then cast shadows too.
- Plan on a 3D model (Plan on a 3D Model), e.g. from drone images. Everything contained in the model is taken into account as a shadow caster.
Under Shading, turn on the Shading Simulation.
Wait until Calculating shading… has finished.

autarc then calculates, for every position of the sun during the year, what share of each module lies in shadow. A shadow only removes the direct light – diffuse light from the sky still reaches the module. The yield is therefore reduced hour by hour by the shaded share of the direct light.

You can see the result directly in the planning:

Panel Shading: each module is coloured by its share of the year spent in shade.
Shade map: shows which areas of the roof are shaded and how strongly.
Shading objects: shows for each object how much yield removing it would gain (Removing this would gain).

You'll find the detailed Shade Report, with losses per array and per object, in the project's technical documentation.

Power, orientation and tilt

The installed power of your system results from the modules:

Peak power of the system (kWp) = 
number of modules × module power (Pmax (STC))

Orientation and tilt determine how much sunlight reaches the modules. In Germany, a south-facing roof with a tilt of about 30–35° gives the highest annual yield. East and west roofs produce somewhat less over the year, but spread the yield more towards morning and evening – which can increase self-consumption.

Typical yields in Germany compared with the optimum (south, 40°, about 1,060 kWh/kWp per year):

Orientation	Tilt	Yield
South	30°	99 %
South-east / south-west	30°	94 %
East / west	30°	81 %
Flat roof	0°	84 %
North	30°	58 %
South-facing wall	90°	71 %

The values are PVGIS averages for a location in central Germany, without shading from objects. For your project, autarc calculates the yield exactly for your location.

PVGIS calculates this effect for each array from the actual position of the sun in every hour. No flat correction factors are needed.

Frequently asked questions

Why does the yield differ from other tools?

Every tool uses its own weather data, module models and loss assumptions. autarc uses the hourly PVGIS values with your system losses (14 % by default) and the shading in your planning. Differences of a few percent are therefore normal.

The weather itself also varies: the same system produces different amounts of electricity from year to year. In central Germany, according to PVGIS, a south-facing system produced between about 960 and 1,160 kWh/kWp between 2014 and 2023 – roughly ±10 % around the average. autarc uses the reference year 2023, which is close to the long-term average. Tools that use a different year or a multi-year average therefore arrive at slightly different values.

Is shading always included?

Shading from the terrain is always included. Shading from objects only when the Shading Simulation is turned on. When it is off, autarc calculates without object shading.

How is a system calculated that I configure by numbers?

If you don't want to draw a system – e.g. an existing solar system in the Current tab –, choose Configure by numbers when creating the PV planning. For each PV array, enter the System size (kWp), Orientation (compass °) and Tilt (°), and if needed the Layout Dual-sided (east-west) and Shading losses (%). The yield is calculated hour by hour with PVGIS, just like a drawn planning. The Shading losses (%) are deducted equally from every time step. The selected PV module is only used for the offer and presentation and does not affect the yield.

What happens if PVGIS can't be reached?

Then autarc temporarily estimates the yield in a simplified way: power × specific yield at the location (kWh/kWp) × correction factor for orientation and tilt. For Germany, the specific yield per postcode area comes from the PV yield study by Umwelt-Campus Birkenfeld (“Good” value), elsewhere from a nearby reference site; the correction factors come from Energie-Experten. As soon as PVGIS can be reached again, autarc recalculates the yield.

Please get in touch if you have any requests or feedback.

How is the PV yield calculated?